Position control for plunge mechanism

ABSTRACT

Apparatus for controlling the position of a plunge mechanism which is mounted to a cartridge engaging assembly is disclosed herein. The apparatus may be embodied in a cartridge engaging assembly having a plunge mechanism that is moveable between a retracted position and an extended position. The plunge mechanism is provided with a reference mark that moves with the plunge mechanism. A detector is mounted to the cartridge engaging assembly, wherein the detector senses an image of the reference mark and produces an output signal related thereto. A control system is operatively associated with the detector and is responsive to the output signal produced thereby. The control system is also operatively associated with the plunge mechanism so that it regulates the position of the plunge mechanism based on the output signal.

FIELD OF THE INVENTION

[0001] The invention pertains to the field of cartridge engagingassemblies (i.e., “pickers”) of the type used in multiple cartridge datastorage systems, and more specifically, to a method and apparatus forcontrolling the position of a plunge mechanism which is mounted to acartridge engaging assembly.

BACKGROUND OF THE INVENTION

[0002] There are many types of data storage systems available today.Some of these systems store data cartridges at known locations, andretrieve desired data cartridges from the known locations so that datamay be written to or read from the data cartridges. Such data storagesystems are often referred to as “juke box” data storage systems,particularly if they can accommodate a large number of data cartridges.

[0003] A typical juke box data storage system may include one or moredifferent types of cartridge receiving devices for holding the variousdata cartridges. For example, one type of cartridge receiving device maycomprise a cartridge storage rack or “magazine”, while another type ofcartridge receiving device may comprise a cartridge read/write device or“drive”. The cartridge storage racks or magazines serve to providestorage locations for the data cartridges and are often arranged so thatthey form one or more vertical stacks, although other configurations arepossible. The cartridge read/write device may be located at anyconvenient location within the data storage system.

[0004] The data storage system may also be provided with a movablecartridge engaging assembly or “picker” for transporting the datacartridges between the various cartridge receiving devices (e.g.,between the cartridge storage racks and the cartridge read/writedevices). A typical cartridge engaging assembly may also be providedwith a plunge mechanism or “thumb assembly” for engaging the variousdata cartridges contained in the cartridge receiving devices and fordrawing them into the cartridge engaging assembly. A positioning systemassociated with the cartridge engaging assembly may be used to move thecartridge engaging assembly between the various cartridge receivingdevices.

[0005] Data storage systems of the type described above are usuallyconnected to a host computer system which may be used to access or storedata on the data cartridges. For example, if the host computer systemissues a request for data contained on a particular data cartridge, acontrol system associated with the data storage system will actuate thepositioning system to move the cartridge engaging assembly along thecartridge storage racks until the cartridge engaging assembly ispositioned adjacent the desired data cartridge. The plunge mechanismassociated with the cartridge engaging assembly may then extend toremove the data cartridge from its cartridge storage rack, and thenretract to draw the cartridge into the cartridge engaging assembly. Thepositioning system may then be actuated to move the cartridge engagingassembly to an appropriate cartridge read/write device. Once properlypositioned adjacent the cartridge read/write device, the plungemechanism may extend to insert the selected data cartridge into thecartridge read/write device so that the host computer may thereafterread data from or write data to the data cartridge. After the read/writeoperation is complete, the plunge mechanism may be actuated to removethe data cartridge from the cartridge read/write device. The cartridgeengaging assembly may thereafter return the data cartridge to itscartridge storage rack.

[0006] A typical plunge mechanism is usually slidably mounted to thecartridge engaging assembly and is provided with a drive system so thatthe plunge mechanism may be moved toward and away from a cartridgeaccess end of the cartridge engaging assembly (i.e., to an extended orretracted position). For example, if it is desired to retrieve a datacartridge from a cartridge receiving device, the drive system moves theplunge mechanism toward the cartridge access end of the cartridgeengaging assembly so that the plunge mechanism may engage (or grab) thedata cartridge. The drive system then retracts the plunge mechanism andpulls the engaged data cartridge into the cartridge engaging assembly.If it is desired to load the data cartridge into the cartridge receivingdevice, the drive system then moves the plunge mechanism and datacartridge toward the cartridge access end of the cartridge engagingassembly, thus inserting the data cartridge into the cartridge receivingdevice.

[0007] Typically, the position of the plunge mechanism must becontrolled within fairly tight tolerances, especially when the plungemechanism is moved to its extended position. Otherwise, the plungemechanism may not be able to adequately engage a data cartridge, or theplunge mechanism may fail to seat a data cartridge in a cartridgereceiving device. One method of controlling the position of a plungemechanism is disclosed in U.S. Pat. No. 6,104,693, entitled “MountingSystem for Cartridge Plunge Mechanism”, which is hereby incorporated byreference for all that it discloses. The method disclosed therein uses adetector assembly to read a plurality of index marks on an elongatelinear reference member. The detector assembly is mounted to the body ofa plunge mechanism, and the reference member is mounted to the frame ofthe cartridge engaging assembly. In this manner, movement of the plungemechanism causes the detector assembly to pass by the plurality of indexmarks on the reference member. The position of the plunge mechanism maytherefore be controlled, for example, by counting the number of indexmarks which the plunge mechanism passes, and controlling the drivesystem for the plunge mechanism in response thereto.

SUMMARY OF THE INVENTION

[0008] New methods and apparatus for controlling the position of aplunge mechanism which is mounted to a cartridge engaging assembly aredisclosed herein.

[0009] In one embodiment, a cartridge engaging assembly comprises aplunge mechanism which is mounted to the cartridge engaging assembly.The plunge mechanism is movable between a retracted position and anextended position. A reference mark is provided on the plunge mechanismso that the reference mark moves with the plunge mechanism. A detectoris also mounted to the cartridge engaging assembly. As the plungemechanism is extended, the detector detects the reference mark andproduces an output signal which is related thereto. A control system isoperatively associated with the detector and is responsive to the outputsignal produced thereby. The control system is also operativelyassociated with the plunge mechanism. As a result, the control systemcan regulate the position of the plunge mechanism based on the outputsignal produced by the detector.

[0010] In another embodiment, a method for regulating a position of aplunge mechanism which is associated with a cartridge engaging assemblycomprises 1) providing a reference mark on the plunge mechanism, 2)detecting a size of the reference mark on the plunge mechanism, and 3)determining the position of the plunge mechanism based on the size ofthe detected reference mark.

[0011] In another embodiment, a method for moving a plunge mechanism toan extended position within a cartridge engaging assembly comprisesinitiating movement of the plunge mechanism from a retracted toward anextended position in accordance with an open loop control schedule. Adetector is monitored to determine when a reference mark provided on theplunge mechanism is detected. Control of the movement of the plungemechanism is then switched to a closed loop control schedule when thedetector detects the reference mark provided on the plunge mechanism.

[0012] In yet another embodiment, a method for moving a plunge mechanismto an extended position within a cartridge engaging assembly comprisesinitiating movement of the plunge mechanism from a retracted toward anextended position in accordance with an open loop control schedule.After the plunge mechanism is moved for a predetermined distance,control of the movement of the plunge mechanism is switched to a closedloop control schedule, and an output signal of a detector which detectsa reference mark provided on the plunge mechanism is monitored.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Illustrative and presently preferred embodiments of the inventionare illustrated in the drawings, in which:

[0014]FIG. 1 is a plan view of a cartridge engaging assembly as it maybe used in a data storage system to access and transport data cartridgescontained within the data storage system;

[0015]FIG. 2 is a first perspective view of the cartridge engagingassembly shown in FIG. 1;

[0016]FIG. 3 is a second perspective view of the cartridge engagingassembly shown in FIG. 2, wherein a side member is removed to show thearrangement of a rack and pinion drive system for moving the assembly'splunge mechanism;

[0017]FIG. 4 is a third perspective view of the cartridge engagingassembly shown in FIG. 2, wherein a side member is removed to show thearrangement of a guide track for the assembly's plunge mechanism andfinger assembly;

[0018]FIG. 5 is a simplified rear elevational view of the cartridgeengaging assembly shown in FIG. 2, wherein the assembly's frame isbroken away to reveal the rear of the assembly's plunge mechanism;

[0019]FIGS. 6a & 6 b are simplified side elevational views of thecartridge engaging assembly shown in FIG. 2, wherein FIG. 6a shows theassembly's plunge mechanism in its retracted position, and wherein FIG.6b shows the assembly's plunge mechanism in its extended position;

[0020]FIG. 7 is an enlarged cross-sectional, elevational view of theFIG. 2 plunge mechanism and its guide rail assembly, wherein theengagement of the bearing members of first and second flange memberswith various guide rails is more clearly shown;

[0021]FIG. 8 is an enlarged side view of the first flange member of theFIG. 2 plunge mechanism;

[0022]FIG. 9 is an enlarged side view of the second, C-shaped flangemember of the FIG. 2 plunge mechanism;

[0023]FIG. 10 is an illustration of how the reference mark provided onthe FIG. 2 plunge mechanism is detected by a detector;

[0024]FIG. 11 is a first exemplary embodiment of a reference mark whichmay be provided on the FIG. 2 plunge mechanism;

[0025]FIG. 12 is a second exemplary embodiment of a reference mark whichmay be provided on the FIG. 2 plunge mechanism; and

[0026]FIG. 13 is a block diagram illustrating a control system'sresponse to the detector and plunge mechanism shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027] A cartridge engaging assembly or “picker” 10 is shown in FIG. 1as it could be used in a “juke box” data storage system 12 to transferdata cartridges 14 between one or more cartridge receiving devices, suchas one or more cartridge storage racks or “magazines” 16, and one ormore cartridge read/write devices or “drives” 18. The various cartridgereceiving devices (e.g., the cartridge storage racks 16 and thecartridge read/write devices 18) may be positioned at various locationswithin the data storage system 12 so that they define a generallyU-shaped configuration, as best seen in FIG. 1. However, the cartridgeengaging assembly 10 may be used in any of a wide range of other typesof data storage systems. For example, the cartridge engaging assembly 10may also be utilized in a data storage system of the type shown anddescribed in U.S. Pat. No. 5,596,556, entitled “Linear Displacement andSupport Apparatus for use in a Cartridge Handling System”, which ishereby incorporated by reference for all that it discloses.

[0028] The cartridge engaging assembly 10 is adapted to 1) engage a datacartridge 14 contained in a cartridge receiving device 16, 18, and then2) draw the data cartridge 14 into the cartridge engaging assembly fortransport to a different cartridge receiving device 16, 18. Movement ofthe cartridge engaging assembly 10 may be achieved via an actuatorsystem 36 which moves the cartridge engaging assembly 10 along aU-shaped path of a cartridge positioning system 22.

[0029] Referring primarily to FIGS. 2-4, the cartridge engaging assembly10 may comprise a frame assembly 38 that defines a chamber or cavity 44sized to receive the data cartridge 14. A plunge mechanism or “thumbassembly” 40 is slidably mounted to the frame assembly 38 so that theplunge mechanism 40 may be moved toward and away from the cartridgeaccess end 46 of the frame assembly 38, generally in the directionsindicated by arrows 54 and 55, respectively (FIG. 3). More specifically,the plunge mechanism 40 may be moved between a retracted position (shownin FIGS. 3-5 and 6(a)) and an extended position (shown in FIG. 6(b)).

[0030] In one preferred embodiment, the mounting system used to slidablymount the plunge mechanism 40 to the frame assembly 38 comprises a firstguide rail 79 positioned on a first side member 70 of the frame assembly38, and a second guide rail 76 positioned on a second side member 72 ofthe frame assembly 38 (FIGS. 3 and 4). The first guide rail 79 comprisesa first horizontal surface 80, and the second guide rail 76 comprises asecond horizontal surface 88. The plunge mechanism 40 comprises a firstflange member 78 for slidably engaging the first horizontal surface 80of the first guide rail 79, and a second, C-shaped flange member 84 forslidably engaging the second horizontal surface 88 of the second guiderail 76. The mounting system guides the plunge mechanism 40 along ahorizontal plane and allows it to be moved toward and away from thecartridge access end 46 of the frame assembly 38, generally in thedirections of arrows 54 and 55, respectively.

[0031] A rack and pinion drive assembly 42 is used to move the plungemechanism 40 back and forth between its retracted position and theextended position. Essentially, the rack and pinion drive assembly 42may comprise a gear rack 48 mounted to the first side member 70 of theframe assembly 38, and a pinion gear 50 mounted to the plunge mechanism40. The pinion gear 50 is mounted to the plunge mechanism 40 so that thepinion gear 50 engages the gear rack 48, as best seen in FIGS. 3, 6(a)and 6(b). A drive system 52 connected to the pinion gear 50 rotates thepinion gear 50 to move the plunge mechanism 40 toward and away from thecartridge access end 46 of the frame assembly 38 (i.e., generally in thedirections indicated by arrows 54 and 55, respectively).

[0032] The engagement of the pinion gear 50 with the gear rack 48defines a vertical guide surface or plane 97, as best seen in FIG. 7.This vertical guide surface or plane 97, together with the second orC-shaped flange member 84 on the plunge mechanism 40 and the second sidemember 72, limits the side-to-side movement (indicated by arrows 21) ofthe plunge mechanism 40.

[0033] The plunge mechanism 40 may also be provided with a fingerassembly 56 which is configured to engage a notch 15 or other similarfeature provided on a data cartridge 14, as best seen in FIG. 6b. Thefinger assembly 56 allows the plunge mechanism 40 to engage and withdrawa data cartridge 14 from a cartridge receiving device 16, 18. In onepreferred embodiment, the finger assembly 56 is actuated by a guidetrack 58 in the frame assembly 38, as best seen in FIG. 4.

[0034] The cartridge engaging assembly 10 may also be provided with aposition control system 62 for providing an output signal from whichinformation may be derived about the position of the plunge mechanism 40in the frame assembly 38. The position control system 62 comprises areference mark 66 which is applied to the plunge mechanism 40 so that itmoves with the plunge mechanism 40 (see FIGS. 5, 6(a) and 6(b)). Adetector 68 mounted to the frame assembly 38 detects the reference mark66 on the plunge mechanism 40 and produces an output signal which isindicative of the size of the reference mark 66. The size of thereference mark may then be used by a picker control system 64 todetermine the position of the plunge mechanism 40. The picker controlsystem 64 may then control the drive system 52 to precisely move theplunge mechanism 40 to a desired position.

[0035] The cartridge engaging assembly 10 may be operated as follows toretrieve a data cartridge 14 from a selected cartridge receiving device(e.g., either the cartridge storage rack 16 or the cartridge read/writedevice 18, as the case may be). Assuming that the cartridge positioningsystem 22 (FIG. 1) has positioned the cartridge engaging assembly 10adjacent the selected data cartridge 14, the picker control system 64may actuate the drive system 52 to rotate the pinion gear 50 so as tomove the plunge mechanism 40 toward the cartridge access end 46 of theframe assembly 38. That is, the drive system 52 moves the plungemechanism 40 in the direction of arrow 54. As the plunge mechanism 40approaches the data cartridge 14, the finger assembly 56 engages thenotch 15 or other similar feature on the data cartridge 14 (FIG. 6(b)).By detecting the reference mark 66 as the plunge mechanism 40 approachesthe data cartridge 14, the position control system 62 may be used toprecisely position the plunge mechanism 40 via the drive system 52. Thearrangement of the plunge mechanism 40 and finger assembly 56 is suchthat the finger assembly 56 engages the notch 15 on the data cartridge14 when the plunge mechanism 40 is at or near its fully extendedposition. This condition is illustrated in FIG. 6b. After the datacartridge 14 has been engaged by the finger assembly 56, the pickercontrol system 64 may operate the drive system 52 to reverse thedirection of rotation of the pinion gear 50. This causes the plungemechanism 40, along with the engaged cartridge 14, to move in theopposite direction (i.e., in the direction of arrow 55 (FIG. 3)),thereby retracting the plunge mechanism 40 and data cartridge 14 intothe cavity 44 defined by the frame assembly 38. The drive system 52continues to retract the plunge mechanism 40 and engaged data cartridge14 until the data cartridge 14 is drawn into the cavity 44 of the frameassembly 38 by an amount sufficient to allow the positioning system 22(FIG. 1) to move the cartridge engaging assembly 10 to another location.The positioning system 22 may thereafter move the cartridge engagingassembly 10 to a new location.

[0036] Once the cartridge engaging assembly 10 has been properlypositioned adjacent the new location, the picker control system 64 mayagain actuate the drive system 52 to move (i.e., extend) the plungemechanism 40 in the direction of arrow 54. As the plunge mechanism 40moves toward the cartridge access end 46 of the frame assembly 38,surface 60 pushes against the data cartridge 14, thereby pushing thedata cartridge 14 into the selected cartridge receiving device (e.g.,the cartridge storage rack 16 or the cartridge read/write device 18, asthe case may be). At the same time, the guide track 58 actuates thefinger assembly 56 to disengage the finger assembly 56 from the notch 15provided in the data cartridge 14. If the plunge mechanism 40 isappropriately extended, the data cartridge 14 will be inserted fullyinto a cartridge receiving device 16, 18 so that it properly “seats” inthe cartridge receiving device 14, 18. Appropriate extension of theplunge mechanism 40 is once again controlled by the position controlsystem 62. After insertion of the data cartridge 14 into a cartridgereceiving device 16, 18, the picker control system 64 may actuate thedrive system 52 once again, to thereby retract the plunge mechanism 40back into the cartridge engaging assembly 10. The cartridge engagingassembly 20 is then ready to withdraw another data cartridge 14 andtransport it to a new location.

[0037] Having briefly described the cartridge engaging assembly 10, aswell as some of its more significant features and advantages, thecartridge engaging assembly 10 will now be described in detail. However,before proceeding with the description, it should be noted that thecartridge engaging assembly 10 may be utilized in any of a wide range ofdata storage systems now known in the art, or that may be developed inthe future, for storing and accessing one or more data cartridges.Accordingly, the present invention should not be regarded as beinglimited to the particular data storage system 12 shown and describedherein. It should also be noted that while the cartridge engagingassembly 10 is shown and described herein as it could be used to storeand retrieve a DLT (digital linear tape) data cartridge 14 having astandard size and configuration, it is not limited to any particulartype or style of data cartridge. Indeed, the cartridge engaging assembly10 could be used with any type of data storage device comprising anytype of data storage medium (e.g., LTO cartridges, magnetic discs ortapes, optical discs, etc.). Consequently, the cartridge engagingassembly 10 should not be regarded as limited to use with the DLT typeof data cartridge 14 shown and described herein.

[0038] With the foregoing considerations in mind, one embodiment of acartridge engaging assembly or “picker” 10 is shown in FIG. 1 as itcould be used in a “juke box” data storage system 12 to transfer datacartridges 14 between one or more cartridge receiving devices, such asone or more cartridge storage racks or “magazines” 16, and one or morecartridge read/write devices or “drives” 18. The various cartridgereceiving devices (e.g., the cartridge storage racks 16 and thecartridge read/write devices 18) may be positioned at various locationswithin the data storage system 12 so that they define a generallyU-shaped configuration, as best seen in FIG. 1, although otherarrangements are possible. By way of example, the cartridge engagingassembly 10 may be utilized in a data storage system of the type shownand described in U.S. Pat. No. 6,025,972, entitled “Multi-PlaneTranslating Cartridge Handling System”, which is hereby incorporated byreference for all that it discloses. Alternatively, the cartridgeengaging assembly 10 may be utilized in a data storage system of thetype shown and described in U.S. Pat. No. 5,596,556 (referred to supra).

[0039] The cartridge engaging assembly 10 is adapted to 1) engage a datacartridge 14 contained in a cartridge receiving device 16, 18, and then2) draw the data cartridge 14 into the cartridge engaging assembly fortransport to a different cartridge receiving device 16,18. Movement ofthe cartridge engaging assembly 10 may be achieved, in part, via anactuator system 36 which moves the cartridge engaging assembly 10 alonga U-shaped path of a cartridge positioning system 22.

[0040] By way of example, the cartridge positioning system 22 may be ofthe type shown and described in U.S. Pat. No. 6,025,972 (referred tosupra). The cartridge positioning system 22 disclosed therein maycomprise a generally rectangularly shaped structure having a pair ofopposed side portions 24 and 26 and an end portion 28. A pair ofcartridge storage racks 16 may be positioned adjacent the two opposedsides 24 and 26 of the cartridge positioning system 22. Similarly, apair of cartridge read/write devices 18 may be positioned adjacent theend 28 of the cartridge positioning system 22.

[0041] The cartridge positioning system 22 may also comprise a lowerplate 23 having a U-shaped guide member or channel 30 formed therein forguiding the cartridge engaging assembly 10 along a generally U-shapedpath 32 so that the cartridge engaging assembly 20 may access the datacartridges 14 contained in the various cartridge storage racks 16 andcartridge read/write devices 18.

[0042] As previously stated, the cartridge engaging assembly 10 may bemoved along the U-shaped guide member 30 by an actuator system 36. Forexample, the actuator system 36 may move the cartridge engaging assembly10 between a first position 17 adjacent the first side portion 24 of thepositioning system 22, a second position 17′ adjacent the end portion 28of the positioning system 22, and a third position 17″ adjacent thesecond side portion 26 of the positioning system 22 (i.e., the cartridgeengaging assembly 10 may be moved along the generally U-shaped path 32).

[0043] The actuator system 36 may comprise a rack and pinion drivesystem having a U-shaped gear rack 34 mounted adjacent the U-shapedguide member 30 in the lower plate 23. A lower pinion gear 31 may bemounted to the cartridge engaging assembly 10 so that it engages theU-shaped gear rack 34. A pair of lower bearing members 33, 35 mounted tothe cartridge engaging assembly 10 may be configured to be received bythe U-shaped guide member 30. The cartridge engaging assembly 10 mayalso be provided with a pair of upper bearing members 37, 39 and anupper pinion gear 41 which engage an upper U-shaped guide member (notshown) and an upper U-shaped gear rack (not shown) provided on an upperplate (not shown) associated with the cartridge positioning system 22. Adrive pinion actuator system 43 may then be used to drive the lower andupper pinion gears 31, 41 to thereby move the cartridge engagingassembly 10 along the U-shaped path 32.

[0044] The foregoing description of the data storage system 12 andcartridge positioning system 22 is provided in order to betterunderstand one environment in which the cartridge engaging assembly 10may be used. However, it should be understood that the cartridgeengaging assembly 10 may be used in any of a wide range of other typesof data storage systems, and in conjunction with any of a wide range ofcartridge positioning systems now known or that may be developed in thefuture. Consequently, the cartridge engaging assembly 10 should not beregarded as being limited to use with the particular data storage system12 and cartridge positioning systems 22 shown and described herein.Also, since detailed descriptions of the data storage system 12 andcartridge positioning system 22 are not required to understand orpractice the cartridge engaging assembly 10, the particular data storagesystem 12 and cartridge positioning system 22 that may be used inconjunction with the cartridge engaging assembly 10 will not bedescribed in further detail herein.

[0045] The details of one embodiment of the cartridge engaging assembly10 are best seen in FIGS. 3-5. Essentially, the cartridge engagingassembly 10 may include a frame assembly 38 having a first side member70 and a second side member 72. The two side members 70, 72 of the frameassembly 38 define a chamber or cavity 44 of sufficient size to receivea data cartridge 14. The plunge mechanism 40 is slidably mounted to theframe assembly 38 so that the plunge mechanism 40 may be moved towardand away from the cartridge access end 46 of the frame assembly 38,generally in the directions of arrows 54 and 55, respectively (FIG. 3).More specifically, the plunge mechanism 40 is slidably mounted to theframe assembly 38 so that the plunge mechanism 40 can be moved between aretracted position (shown in FIGS. 3, 4, and 6(a)) and an extendedposition (shown in FIG. 6(b)).

[0046] In one preferred embodiment, the plunge mechanism 40 may bemounted on first and second elongate guide rails 79 and 76 that arerespectively provided on the first and second sides 70, 72 of the frameassembly 38. The first elongate guide rail 79 includes a firsthorizontal guide surface 80, whereas the second elongate guide rail 76includes a second horizontal guide surface 88. In one preferredembodiment, the first and second horizontal guide surfaces 80, 88 arenon-coplanar, as best seen in FIG. 7. Alternatively, the first andsecond horizontal guide surfaces 80, 88 may be coplanar. In any event,the main body portion 96 of the plunge mechanism 40 may include a firstflange member 78 which is sized and positioned to engage the firsthorizontal guide surface 80 of the first elongate guide rail 79. Themain body portion 96 of the plunge mechanism 40 may also include asecond or C-shaped flange member 84 which is adapted to engage thesecond horizontal guide surface 88 of the second elongate guide rail 76.

[0047] Referring now primarily to FIGS. 7 and 8, the first flange member78 may comprise a generally rectangularly shaped member having a bottomsurface 25 and a top surface 27. A first or lower bearing member 75 isprovided on the bottom surface 25 of the first flange member 78 so thatit may contact the first horizontal guide surface 80, as best seen inFIG. 7. The top surface 27 of the flange member 78 may be provided withan upper bearing member 77. The upper bearing member 77 is positioned sothat it may contact a horizontal capture rail 74. The first flangemember 78 may also be provided with a pair of vertical bearing members71, 73 which are positioned so that they may contact the first sidemember 70. However, as will be explained in greater detail below, theupper bearing member 77 and pair of vertical bearing members 71, 73 donot normally contact their respective adjacent surfaces.

[0048] The second flange member 84 may comprise a substantially C-shapedmember and is best seen in FIGS. 7 and 9. Essentially, the second flangemember 84 comprises a lower horizontal member 45 and an upper horizontalmember 47. The bottom facing surface 93 of the upper horizontal member47 may be provided with a pair of bearing members 89, 91 which arepositioned in spaced-apart relation. The pair of bearing members 89, 91contact the second horizontal surface 88 on the second guide rail 76, asbest seen in FIG. 7. Additionally, the lower horizontal member 45 may beprovided with a plurality of bearing members. More specifically, thelower horizontal member 45 may be provided with a pair of verticalbearing members 81, 83 which are positioned so that they may contact thesecond side member 72. The upper facing surface 95 of the lowerhorizontal member 45 may be provided with a pair of bearing members 85,87 which are positioned so that they may contact the bottom surface 90of the second guide rail 76. The various bearing members 81, 83, 85, 87which are provided on the lower horizontal member 45 do not normallycontact their respective adjacent surfaces.

[0049] In accordance with the structural arrangement described above,the plunge mechanism 40 is supported on one side by the bearing member75 that contacts the first horizontal surface 80, and on the other sideby the bearing members 89, 91 that contact the second horizontal surface88. The three bearing members 75, 89, 91 allow the plunge mechanism 40to be moved along a defined horizontal plane (not shown), even thoughthe bearing members 75, 89, 91 themselves may be non-coplanar.

[0050] The side-to-side movement of the plunge mechanism 40 (e.g.,movement in the directions indicated by arrows 21 (FIG. 7)) is limitedby a combination of the engagement of the pinion gear 50 and gear rack48 on the one side, and on the other side by the pair of verticalbearing members 81, 83 and the second side member 72. More specifically,the engagement of the pinion gear 50 and the gear rack 48 defines avertical guide surface or plane 97 which limits the maximum leftward(looking at FIG. 7) movement of the plunge mechanism 40. The maximumrightward movement of the plunge mechanism 40 is limited by the pair ofvertical bearing members 81 and 83 contacting the second side member 72,wherein the second side member 72 defines a second vertical guidesurface or plane. As will be described in greater detail below, it isgenerally preferred that spaces or gaps be provided between the pair ofvertical bearing members 81, 83 and the side member 72 to preventbinding of the pinion gear 50 and gear rack 48 (FIG. 7).

[0051] Recognizing that the pinion gear 50 and gear rack 48 will wearwith use, the first flange member 78 may be provided with the pair ofvertical bearing members 71, 73 which may eventually contact the firstside member 70. The pair of vertical bearing members 71, 73 therebylimit the maximum leftward movement of the plunge mechanism 40 even ifthe pinion gear 50 and gear rack 48 experience excessive wear. Putanother way, the maximum side-to-side movement (arrows 21) of the plungemechanism 40 generally will not exceed the sum of the spaces or gapsprovided between the pair of vertical bearing members 71, 73 and thefirst side member 71 on the one side of plunge mechanism 40, and thepair of vertical bearing members 81, 83 and the second side member 72 onthe other side of plunge mechanism 40.

[0052] The various spaces or gaps provided between the first pair ofvertical bearing members 71, 73 and the first side member 71, andprovided between the second pair of vertical bearing members 81, 83 andthe second side member 72, may comprise any of a wide range of sizesdepending on the amount of horizontal positioning accuracy that is to beprovided for the plunge mechanism 40. In one preferred embodiment, thespaces or gaps provided between the vertical bearing members 71, 73 andthe first side member 70 may be in the range of about 0.10 mm to 0.60 mm(0.35 mm preferred). Similarly, the spaces or gaps provided between thesecond pair of vertical bearing members 81, 83 and the second sidemember 72 may be in the range of about 0.01 mm to 0.61 mm (0.3 mmpreferred).

[0053] In one preferred embodiment, the first side member 70 may also beprovided with the capture rail 74 to prevent excessive upward verticalmovement of the first flange member 78. Excessive upward verticalmovement of the second or C-shaped flange member 84 is provided by thelower surface 90 of the second guide rail 76.

[0054] The bearing member 77 on the first flange member 78, and thebearing members 85, 87 on the lower horizontal member 45 of the secondflange member 84, will contact the capture rail 74 and lower surface 90of the second guide rail 76, respectively, should the condition developwherein the plunge mechanism 40 is urged upward.

[0055] It is generally preferred that spaces or gaps be provided betweenthe bearing member 77 and the capture rail 74 on the one side of theplunge mechanism 40, and the bearing members 85, 87 and the lowersurface 90 of the second guide rail 76 on the other side of the plungemechanism 40. The various spaces or gaps may comprise any of a widerange of sizes depending on the amount of vertical positioning accuracythat is to be provided for the plunge mechanism 40. In one preferredembodiment, the spaces or gaps provided between the bearing members 77and the capture rail 74 may be in the range of about 0.05 mm to 0.45 mm(0.25 mm preferred). Similarly, the spaces or gaps provided between thebearing members 85, 87 and the lower surface 90 of the second guide rail76 may be in the range of about 0.05 mm to 0.45 mm (0.25 mm preferred).

[0056] The various components of the mounting system just described maybe made from any of a wide range of materials which are suitable for anintended application. For example, in one preferred embodiment, thefirst and second side members 70, 72 of the frame assembly 38 are moldedfrom polycarbonate plastic, although other materials may also be used.It is preferred, but not required, that the various guide rails (e.g.,the first and second guide rails 79, 76, as well as the capture rail 74)associated with the first and second side members 70, 72 be provided asintegral components thereof, thus eliminating the need to separatelyattach and align these components to the two side members 70, 72. Forexample, in one preferred embodiment wherein both of the side members70, 72 are molded from polycarbonate plastic, the first guide rail 79,second guide rail 76, and capture rail 74 are molded into the first andsecond side members 70, 72 of the frame assembly 38, as best seen inFIGS. 3 and 4.

[0057] The main body portion 96 of the plunge mechanism 40 may also bemade from any of a wide range of materials which are suitable for anintended application, such as metals or plastics. For example, in onepreferred embodiment, the main body portion 96 of the plunge mechanism40 is molded from nylon, although other materials could also be used.The various bearing members 71, 73, 75, etc. provided on the first andsecond flange members 78, 84 of the main body 96 of the plunge mechanism40 may comprise integral portions of the respective flange members 78,84. Alternatively, the various bearing members 71, 73, 75, etc. may beprovided as separate components which are fixedly attached to the firstand second flange members 78, 84 at appropriate positions. If so, thevarious bearing members 71, 73, 75, etc. may be fabricated from any of awide range of materials (such as Teflon.RTM.) which are suitable forproviding a low friction engagement with the various surfaces of thevarious guide rails.

[0058] As mentioned above, the plunge mechanism 40 is moved between itsretracted and extended positions by a rack and pinion drive assembly 42,as best seen in FIG. 3. Essentially, the rack and pinion drive assembly42 comprises an elongate gear rack 48 that is affixed to the first sidemember 70 of the frame assembly 38 at a convenient position. Forexample, in one preferred embodiment, the gear rack 48 is affixed to thefirst side member 70 at a position which is immediately below thehorizontal guide surface 80. Alternatively, the gear rack 48 may beaffixed elsewhere on the first side member 70, or to the second sidemember 72.

[0059] The gear rack 48 may be made from any of a wide range ofmaterials which are suitable for an intended application, such as metalsor plastics. In the embodiment shown and described herein, wherein thefirst side member 70 of the frame assembly 38 comprises molded plastic,the gear rack 48 may comprise an integral component of the first sidemember 70 (i.e., the gear rack 48 comprises a molded portion of thefirst side member 70). Alternatively, the gear rack 48 may comprise aseparate component which is fixedly mounted to the first side member 70.

[0060] The main body portion 96 of the plunge mechanism 40 is providedwith a pinion gear 50 which is positioned so that it engages the gearrack 48. See FIGS. 3, 6(a) and 6(b). The pinion gear 50 is caused torotate by a drive system 52 which, in one preferred embodiment, includesa motor 98 and a gear reduction system 94. The motor 98 may be mountedto the main body portion 96 of the plunge mechanism 40 such that it isoperatively associated with the gear reduction system 94. In thismanner, the motor 98 rotates the pinion gear 50 to extend and retractthe plunge mechanism 40.

[0061] The motor 98 may comprise any of a wide range of motors which aresuitable for an intended application. In one preferred embodiment, themotor 98 comprises a permanent magnet d.c. motor such as Model No.RS-385PH, available from Mobuchi Corp. of China. However, other motortypes may also be used.

[0062] The gear reduction system 94 may comprise a conventional gearreduction system which utilizes a plurality of spur gears to provide areduction ratio sufficient to allow the motor 98 to extend and retractthe plunge mechanism 40 at an appropriate speed and with sufficientforce to withdraw and insert the data cartridge 14 into a selectedcartridge receiving device 16, 18. In one preferred embodiment, the gearreduction system 94 provides a reduction ratio of about 11.5:1, althoughother ratios may be used depending on the speed and torquecharacteristics of a particular motor 98. The various spur gears of thegear reduction system 94 may be made from any material which is suitablefor an intended application, such as metal or plastic. In one preferredembodiment, the various spur gears of the gear reduction system 94 aremade from brass and stainless steel. Alternatively, the gear reductionsystem 94 could utilize other types of gears to provide the desiredreduction, such as worm gears.

[0063] The plunge mechanism 40 may also be provided with any of a widevariety of finger assemblies which are well-known in the art forengaging data cartridges such as data cartridge 14. Accordingly, thefinger assembly should not be regarded as limited to any particular typeof finger assembly. By way of example, in one preferred embodiment, thefinger assembly 56 may comprise an arm 57 having a hook portion 59. Thehook portion 59 of the arm 57 is configured to engage a notch 15 (FIGS.6(a), 6(b)) which is provided on a data cartridge 14. The arm 57 ispivotally mounted to the main body 96 of the plunge mechanism 40 so thatthe arm 57 is free to pivot about a pivot axis 61. A spring 63 biasesthe arm toward the engaged position shown in FIGS. 3 and 6(a). The arm57 may be provided with a pin 65 which engages the guide track 58provided on the second side 72 of the frame assembly 38 (FIG. 4). Theguide track 58 actuates the arm 57 as the plunge mechanism 40 moves backand forth between its retracted position (FIGS. 3, 4 & 6(a)) and itsextended position (FIG. 6(b)).

[0064] However, since finger and track systems for engaging datacartridges 14 are well-known in the art and could be easily provided bypersons having ordinary skill in the art after having become familiarwith the teachings disclosed herein, the particular finger system 56 andguide track 58 disclosed above will not be described in greater detailherein.

[0065] The cartridge engaging assembly 10 may also be provided with aposition control system 62 for providing an output signal from whichinformation may be derived about the position of the plunge mechanism 40in the frame assembly 38. The position control system 62 comprises areference mark 66 which is applied to the plunge mechanism 40 so that itmoves with the plunge mechanism 40. A detector 68 mounted to the frameassembly 38 detects the reference mark 66 on the plunge mechanism 40 andproduces an output signal which is indicative of the size of thereference mark 66. The size of the reference mark may then be used by apicker control system 64 to determine the position of the plungemechanism 40. The picker control system 64 may then control the drivesystem 52 to precisely move the plunge mechanism 40 to a desiredposition.

[0066] The reference mark 66 may comprise any of a wide range of marks.By way of example, the mark 66 in one preferred embodiment may comprisea pair of horizontal bars separated by a gap (i.e., a pair of barspositioned in spaced-apart relation; FIG. 11). However, the referencemark 66 could also consist of a single bar (FIG. 12), or comprise anynumber of bars. Likewise, the mark could comprise indicia other thanbars.

[0067] The reference mark 66 may be applied to the plunge mechanism 40in a number of ways. In a preferred embodiment, the reference mark 66may be applied to a sticker which, in turn, is applied to the plungemechanism 40 (FIG. 5). In another embodiment, the reference mark 66 maybe formed by a recess or boss on the plunge mechanism 40 (not shown). Inyet another embodiment, the reference mark 66 may comprise anyidentifiable edge, mark, etc. which appears on the plunge mechanism 40as a result of its manufacture. (Note that the reference mark 66 may begenerally referred to in the claims as a “reference means”.) Thereference mark 66 is preferably constructed and applied to the plungemechanism 40 such that at a least a portion of the reference mark 66 maybe easily and clearly detected by the detector 68.

[0068] To enable detection of the reference mark 66 by the detector 68,a light source 67 may need to illuminate the reference mark 66. Ideally,the reference mark 66 receives enough illumination from ambient lightsources (e.g., through the cartridge access end 46 of the cartridgeengaging assembly 10). However, it is envisioned that such is not oftenthe case. A light source 67 may therefore be mounted to the cartridgeengaging assembly 10 such that light is projected onto the referencemark 66. In FIG. 4, the light source 67 is mounted on the second sidemember 72 of the frame assembly 38. However, the light source 67 may bevariously mounted, and may, for example, be mounted in either astationary position (as shown in FIG. 4) or in a location which travelswith the plunge mechanism 40 (e.g., a light source might be mounteddirectly on the plunge mechanism (not shown)). A preferred embodiment ofa light source 67 may comprise a plurality of light emitting diodes(LEDs) 69 which emit light through a lens 99.

[0069] The detector 68 is mounted to the cartridge engaging assembly 10such that it is capable of sensing the reference mark 66. One way inwhich the detector 68 may sense the reference mark 66 is via a chargecoupled device (CCD) 102. Depending on where the detector 68 is mounted,the detector 68 may require a lens 104 or lenses for aligning and/orfocusing an image of the reference mark 66 onto a device such as theafore-mentioned CCD 102.

[0070] In FIG. 4, the detector 68 is mounted on the second side member72 of the frame assembly 38. Although the detector 68 may be variouslymounted, it should be mounted such that travel of the plunge mechanism40 causes the reference mark 66 to be sensed differently by the detector68. For example, movement of the plunge mechanism 40 with respect to thedetector 68 may cause an image of the reference mark 66 which is sensedby the detector 68 to change in size (i.e., the image is sensed by avarying number of pixels of a CCD 102).

[0071] If the detector 68 comprises a CCD 102 and lens 104 asillustrated in FIG. 4, then the position of the plunge mechanism 40 inthe cartridge engaging assembly 10 may be determined as a function ofthe distance between the lens 104 and the reference mark 66. Thedistance between the lens 104 and the reference mark 66 may bedetermined using the following formula (FIG. 10):

M=H″/H=S″/S  (1)

[0072] In the above formula, M is the magnification of the lens 104. Thequantity H is a known measurement of the reference mark 66 (e.g., thespace between the two horizontal bars of the reference mark 66 (FIG.11)). The quantity H″ is a calculable measurement of the image which issensed by the detector 68 (e.g., the number of pixels representing thespace H between the two horizontal bars of the reference mark 66). Thequantity S″ is the distance between the lens principle point and apredetermined point of the image sensed by the detector 68 (wherein thepredetermined point of the image corresponds to a similar point of thereference mark 66). The quantity S is an unknown representing thedistance between the lens principle point and a predetermined point onthe reference mark 66. Given that all quantities but S are either knownor are independently calculable, the unknown S can be computed using thefollowing formula:

S=HS″/H″  (2)

[0073] Once S has been computed, then 1) a known position of thedetector 68 with respect to the cartridge engaging assembly 10, and 2) aknown position of the reference mark 66 with respect to the plungemechanism 40, may be used to compute the position of the plungemechanism 40 with respect to the cartridge engaging assembly 10.

[0074] The above computations may be performed by either the detector 68or the picker control system 64. If the computations are performed bythe detector 68, then the detector 68 may generate an output signalwhich is indicative of the position of the plunge mechanism 40. However,if the computations are performed by the picker control system 64, thenthe detector 68 may generate an output signal comprising image pixeldata. In either case, the picker control system 64 may use the outputsignal of the detector 68 to derive information about the position ofthe plunge mechanism 40. The position information may then be used tocontrol operation of the drive system 52, and thus control movement ofthe plunge mechanism 40 to a desired position.

[0075] The detector 68 may comprise any of a wide range of CCD and/orother sensor types that are well-known in the art and readilycommercially available. Preferably, the CCD 102 is a linear CCD or barcode reader. As such, the bar code reader can not only be used to detectthe reference mark 66, but to also read a bar code label which isapplied to a data cartridge 14 located adjacent the cartridge access end46 of the cartridge engaging assembly 10. A bar code reader for readingbar code labels which are applied to data cartridges 14 is disclosed inU.S. patent application Ser. No. 09/716,878, entitled “Dual Bar CodeReading System for a Data Storage System”, which is hereby incorporatedby reference for all that it discloses.

[0076] The data storage system 12 may also be provided with a pickercontrol system 64 (FIG. 13) for coordinating the function and operationof the cartridge engaging assembly 10, as well as the function andoperation of the cartridge positioning system 22 and actuator system 36.In FIG. 13, the detector 68 is shown to receive the reference mark 66(i.e., in the form of an image). The detector 68 then generates anoutput signal which is provided to the control system 64. The controlsystem 64 uses the output signal to determine the position of the plungemechanism 40. The control system 64 then provides a signal (e.g., avoltage of limited duration) to the plunge mechanism 40 to controlmovement thereof (i.e., to regulate the position of the plunge mechanism40). Detection of the reference mark 66 and control of the plungemechanism's movement continues until the control system 64 determinesthat a detected size of the reference mark 66 is indicative of theplunge mechanism 40 being in a final and desired position (e.g., anextended position).

[0077] Since picker control systems 64 are well-known in the art andcould be easily provided by persons having ordinary skill in the artafter having become familiar with the teachings disclosed herein, aparticular picker control system 64 will not be described in furtherdetail herein.

[0078] The cartridge engaging assembly 10 may be operated as follows toretrieve and load a data cartridge 14 from and to a selected cartridgereceiving device (e.g., either the cartridge storage rack 14 or thecartridge read/write device 18, as the case may be). Assuming that thecartridge positioning system 22 has positioned the cartridge engagingassembly 10 adjacent a selected data cartridge 14, the picker controlsystem 64 may actuate the drive system 52 to rotate the pinion gear 50to move the plunge mechanism 40 toward the cartridge access end 46 ofthe frame assembly 38 (i.e., in the direction of arrow 54). As theplunge mechanism 40 approaches the data cartridge 14, the fingerassembly 56 engages a notch 15 or other similar feature on the datacartridge 14 (FIG. 6(b)). By detecting the reference mark 66 as theplunge mechanism 40 approaches the data cartridge 14, the positioncontrol system 62 may be used to precisely position the plunge mechanism40 via the drive system 52. The arrangement of the plunge mechanism 40and finger assembly 56 is such that the finger assembly 56 engages thenotch 15 on the data cartridge 14 when the plunge mechanism 40 is at ornear its fully extended position. This condition is illustrated in FIG.6b. After the data cartridge 14 has been engaged by the hook portion 59of the finger assembly 56, the picker control system 64 may operate thedrive system 52 to reverse the direction of rotation of the pinion gear50. This causes the plunge mechanism 40, along with the engagedcartridge 14, to move in the opposite direction (i.e., in the directionof arrow 55), thereby retracting the plunge mechanism 40 and datacartridge 14 into the cavity 44 defined by the frame assembly 38. Thedrive system 52 continues to retract the plunge mechanism 40 and engageddata cartridge 14 until the data cartridge 14 is drawn into the cavity44 of the frame assembly 38 by an amount sufficient to allow thecartridge positioning system 22 to move the cartridge engaging assembly10 to another position. The cartridge positioning system 22 maythereafter move the cartridge engaging assembly 10 to a new location.

[0079] Once the cartridge engaging assembly 10 has been properlypositioned adjacent a new location, the picker control system 64 mayagain actuate the drive system 52 to move (i.e., extend) the plungemechanism 40 in the direction of arrow 54. As the plunge mechanism 40extends, a surface 60 of the plunge mechanism 40 pushes against the datacartridge 14, thereby pushing the data cartridge 14 into a selectedcartridge receiving device (e.g., the cartridge storage rack 16 or thecartridge read/write device 18, as the case may be). At the same time,the guide track 58 actuates the finger assembly 56 to disengage the hookportion 59 of the finger assembly 56 from the notch 15 provided in thedata cartridge 14. If the plunge mechanism 40 is appropriately extended,the data cartridge 14 will be inserted fully into a cartridge receivingdevice 16, 18 so that it properly “seats” in the cartridge receivingdevice 14, 18. Appropriate extension of the plunge mechanism 40 is onceagain controlled by the position control system 62. Once the plungemechanism 40 is fully extended, the data cartridge 14 will have beeninserted fully into the cartridge receiving device 16, 18. The pickercontrol system 64 may then actuate the drive system 52 to retract theplunge mechanism 40 back into the cartridge engaging assembly 10. Thecartridge engaging assembly 10 is then ready to withdraw another datacartridge 14 and transport it to a new location.

[0080] During the above cartridge retrieval and loading operations, theposition of the plunge mechanism 40 when it is in its extended positionis often critical. For example, under- or over-extension of the plungemechanism 40 during cartridge retrieval can lead to the finger assembly56 being unable to engage the notch 15 on a data cartridge 14. Likewise,under- or over-extension (and particularly under-extension) can lead toa data cartridge 14 failing to properly seat within a selected cartridgereceiving device 16, 18. Such failures to seat can 1) lead to a datacartridge 14 being misread by a cartridge read/write device 18, or 2)lead to a data cartridge 14 becoming dislodged from a cartridgereceiving device 16, 18 (e.g., falling out of the cartridge receivingdevice 16, 18). As a result of these problems, operation of the drivesystem 52 may be controlled by the picker control system 64, aspreviously described, to precisely control the position of the plungemechanism 40.

[0081] Preferably, the drive system 52 first moves the plunge mechanism40 from its retracted position toward its extended position inaccordance with an open loop control schedule. Either 1) in response tomonitoring the detector 68 to determine when the reference mark 66 isdetected, or 2) in response to having moved the plunge mechanism 40 fora predetermined distance, control of the drive system 52 is switched toa closed loop control schedule wherein the plunge mechanism 40 isprecisely positioned in response to the detector's output of a signalwhich is indicative of the position of the plunge mechanism 40.Preferably, the response time of the detector 68 and/or accuracy of thedrive system 52 provide for switching the drive system 52 to its closedloop control schedule during the last five millimeters (5 mm) of plungemechanism plunge. Thus, a relatively small amount of image data needs tobe processed by the detector 68 and/or control system 64.

[0082] As was previously and briefly discussed, one embodiment of thecartridge engaging assembly 10 uses the detector 68 to fulfill multiplefunctions. One function is the detection of the reference mark 66.Another function is the reading of bar code labels which are applied tothe edges of data cartridges 14 adjacent the cartridge access end 46 ofthe cartridge engaging assembly 10. When the plunge mechanism 40 is inits retracted position, the light source 67 illuminates the labels onthe data cartridges 14. In this manner, prior to retrieving a datacartridge 14, the cartridge engaging assembly 10 may verify or detectwhich data cartridge 14 it is retrieving. As the plunge mechanism 40moves to its extended position, the light source 67 begins to illuminatethe reference mark 66 which is applied to the plunge mechanism 40. Inthis manner, the detector 68 can detect the reference mark 66 andprovide an output signal to the picker control system 64 for the purposeof precisely positioning the plunge mechanism 40 with respect to a datacartridge 14.

[0083] While illustrative and presently preferred embodiments of theinvention have been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed, and that the appended claims are intended to be construed toinclude such variations, except as limited by the prior art.

What is claimed is:
 1. A cartridge engaging assembly, comprising: aplunge mechanism that is moveable between a retracted position and anextended position; a reference mark, provided on and moving with theplunge mechanism; a detector to sense an image of the reference mark andproduce an output signal related thereto as the plunge mechanism moveswith respect to the detector; and a control system that is operativelyassociated with the detector and responsive to said output signal; saidcontrol system also being operatively associated with the plungemechanism; said control system regulating the position of the plungemechanism based on the output signal.
 2. The cartridge engaging assemblyof claim 1, wherein the reference mark comprises a pair of barspositioned in spaced-apart relation.
 3. The cartridge engaging assemblyof claim 1, wherein the reference mark consists of a single bar.
 4. Thecartridge engaging assembly of claim 1, wherein the detector comprises abar code reader, said bar code reader: i) sensing an image of thereference mark, and ii) reading a bar code provided on a cartridgepositioned adjacent the cartridge engaging assembly.